Candidate for fixing MacOS SHM

diff --git a/src/ipc/mem/Segment.cc b/src/ipc/mem/Segment.cc
index c2cc40dd7391db644b3b62d784b9b9b21cad9628..33a6ff9c9bd3831d9335ebb56cc5e8deb1c86f54 100644 (file)
--- a/src/ipc/mem/Segment.cc
+++ b/src/ipc/mem/Segment.cc
@@ -88,7 +88,8 @@ Ipc::Mem::Segment::create(const off_t aSize)
     assert(aSize > 0);
     assert(theFD < 0);
 
-    theFD = shm_open(theName.termedBuf(), O_CREAT | O_RDWR | O_TRUNC,
+    // OS X does not allow using O_TRUNC here.
+    theFD = shm_open(theName.termedBuf(), O_CREAT | O_RDWR,
                      S_IRUSR | S_IWUSR);
     if (theFD < 0) {
         debugs(54, 5, HERE << "shm_open " << theName << ": " << xstrerror());
@@ -97,14 +98,19 @@ Ipc::Mem::Segment::create(const off_t aSize)
     }
 
     if (ftruncate(theFD, aSize)) {
-        debugs(54, 5, HERE << "ftruncate " << theName << ": " << xstrerror());
+        const int savedError = errno;
+        unlink();
+        debugs(54, 5, HERE << "ftruncate " << theName << ": " << xstrerr(savedError));
         fatalf("Ipc::Mem::Segment::create failed to ftruncate(%s): %s\n",
-               theName.termedBuf(), xstrerror());
+               theName.termedBuf(), xstrerr(savedError));
     }
+    // We assume that the shm_open(O_CREAT)+ftruncate() combo zeros the segment.
 
-    assert(statSize("Ipc::Mem::Segment::create") == aSize); // paranoid
+    theSize = statSize("Ipc::Mem::Segment::create");
+
+    // OS X will round up to a full page, so not checking for exact size match.
+    assert(theSize >= aSize);
 
-    theSize = aSize;
     theReserved = 0;
     doUnlink = true;